The microencapsulation of a component by self-assembled hollow microspheres is one of the important aspects of nanotechnology and materials science. Control over the shape and composition of the supporting structure, parameters that influence the material properties, is important for many applications, such as diagnostics, drug delivery, electronic displays and catalysis (see Ke at al. Angew. Chem. 2011, 123, 3073; De Cock et al. Angew. Chem. Int. Ed. 2010, 49, 6954; Yang et al. Angew. Chem. 2011, 123, 497; Comiskey et al. Nature 1998, 394, 253; Peyratout at al. Angew. Chem. Int. Ed. 2004, 43, 3762). Preparation of conventional polymeric microcapsules proceeds via a layer-by-layer (L-b-L) scheme, where a solid support is coated by the sequential addition of a series of oppositely charged polyelectrolyte layers (see Caruso et al. Science 1998, 282, 1111; Donath et al, Angew. Chem. Mt. Ed. 1998, 37, 2201). This strategy provides a uniform material but suffers from reduced encapsulation efficiencies due to the solid template. An alternative method utilises colloidal emulsion-templating where liquid-liquid interfaces drive the self-assembly of shell components (see Cui at al. Adv. Funct. Mater. 2010, 20, 1625). However, it is difficult to control monodispersity and material diversity of the resulting microcapsules, thereby limiting its functionality in drug delivery and sensing applications.
In contrast, microfluidic droplets, a subset of colloidal emulsion, have shown great promise for microcapsule fabrication (see Gunther et al. Lab Chip 2006, 6, 1487; Huebner et al. Lab Chip 2008, 8, 1244; Theberge et al. Angew. Chem. Int. Ed. 2010, 49, 5846). These droplets of narrow size distribution (polydispersity index<2%) can be generated at extremely high frequency with economic use of reagents (see Xu et al. AlChE Journal 2006, 52, 3005). Initial efforts to prepare capsules based on microdroplet-assisted fabrication have focused on phase separation using double emulsion and liquid crystal core templating (see Utada et al. Science 2005, 308, 537; Priest at al. Lab Chip 2008, 8, 2182). The formation of polymeric capsule walls has also been described in an approach that involves microfluidic device surface treatment and rapid polymerization techniques (see Zhou at al. Electrophoresis 2009, 31, 2; Abraham et al. Advanced Materials 2008, 20, 2177). The wall is formed as the solvent evaporates from formed organic solvent droplets. Metal-organic framework capsules have also been recently reported (see Ameloot et al. Nat. Chem. 2011, 3, 382). With the current ionic or covalent cross-linking strategies, however, the main challenge in capsule fabrication lies in the simultaneous production of uniform capsules with high cargo loading efficiencies and facile incorporation of diverse functionality into the capsule shell.
The present inventors have now established a capsule based on a cucurbituril-based host-guest network. Designing microstructures using multivalency and cooperativity through molecular recognition provides an unparalleled opportunity in the fabrication of microcapsules with tailorable interactions and functionalities. However, efforts in preparing microcapsules using supramolecular host-guest approach, as described herein, are scarce (see De Cock at al. Angew. Chem. Int. Ed. 2010, 49, 6954).
Previous disclosures include a colloidal microcapsule comprising β-cyclodextrin and modified gold nanoparticles (AuNPs) prepared via emulsion templating (Patra at al., Langmuir 2009, 25, 13852), and a microcapsule comprising polymers functionalized with cyclodextrin and ferrocene prepared using a L-b-L synthesis (Wang et al., Chemistry of Materials 2008, 20, 4194).